Thermostatic switch



July 19, 1949. LQFGREN 2,476,498

THERMOSTATIC SWITCH Filed Oct. 26, 1945.

Patented July 19, 1949 THERMO STATIC SWITCH Einar G. Lofgren, Minneapolis, Minn., assignor to Electro-Mechanical Laboratories, Incorporated, Minneapolis, Minn., a corporation of Minnesota Application October 26, 1945, Serial No. 624,671

4 Claims.

My present invention relates to improvements in thermally-operated switches or thermostats, and more specifically to improvements in thermally-operated switches or thermostats of the rate of change type. As is well known, thermostats of the said more common fixed temperature type operate at preselected fixed temperatures; whereas, thermostats of the said rate of change type towhich the present invention particularly relates. operate as a result of temperature changes exceeding a predetermined rate. Thermostats of this so-called rate of change type are particularly adapted for use as control elements in fire alarm. circuits and the like, since they are unaffected by temperature changes taking place at a normal rate, but respond quickly to abnormally rapid temperature changes such as may be caused by fire in the vicinity of the thermostat or control device.

Among the important objects of the invention is the provision of a very inexpensive but highly eflicient thermostat of the kind last described, and to which end I provide a simplified design involving few parts that can be quickly and inexpensively assembled without the use of tools, jigs, or the like. To the same end, I preferably form the thermostat switch proper of two identical units for the purpose of further reducing the cost of manufacture and assembly.

The above and other highly important objects and advantages of the invention will be made apparent from the following specification, claims, and appended drawings.

In the accompanying drawings, like characters indicate like parts throughout the several views. 1

Referring to the drawings:

Fig. l is a front and top perspective view of a commercial form of thermostat involving the invention;

Fig. 2 is a rear elevation of the device of Fig. 1;

Fig. 3 is a transverse sectional view taken on the line 33 of Fig. 2;

Fig. 4 is a longitudinal sectional view taken on the line 44 of Fig. 2;. and

Fig. 5 is a diagrammatic view illustrating the thermostat connected in an alarm circuit.

The preferred embodiment of the invention illustrated comprises a pair of like thermostat units indicated by I and 2 respectively, and a casing indicated as an entirety by 3 and in which the said units I and 2 are mounted. Each of the units I and 2 comprises a rigid metallic post 4 and a bowed flexible metallic contact strip 5. The posts 4 are each equipped at one end with a cap 6 and at its other end with a cap 1. These caps E and I are centrally apertured to receive the reduced diameter ends 8 of the posts 4, which latter are peened orupset in the manner of a rivet to permanently anchor the caps to the posts. The caps 6 and I are each provided with four longitudinally inwardly diverging wing like flanges 9 forming sockets in their respective caps. One of the flanges 9 of eachof the caps 6 is extended to provide a terminal lug I0 equipped with a terminal screw II The bowed spring contact strip 5 of each of the thermostat units I and 2 is normally straight, but is bowed at the time of assembly and has opposite ends seated against corresponding cap flanges 9 at opposite ends of the post 4 of that unit. The spring contact members 5 are, of course, subject to their own yielding tension to straighten out and elongate, but are held under compression between the opposed cap flanges 9 and are retained against accidental lateral displacement by wedging action therebetween and the posts 4.

The units I- and 2 are mounted with their posts 4 in laterally-spaced parallel relation and the bowed contact strips 5 in opposed normally spaced relation as shown best in Fig. 2, and these units I and Z are preferably turned end-for-end one in respect to the other, whereby to permit the use of identical units I and. 2 without producing the same in rights and lefts and providing maximum spacing of the screw-equipped circuit terminals II).

The units I and 2 may be mounted in various Ways, but are preferably mounted in the casing 3, which forms an important phase of the present invention. This casing 3- comprises a front wall I2 having side wall-formingflanges I3 and end wall-forming flanges I4. This casing 3 is preferably formed of sheet metal and the side walls It thereof are provided with outturned anchoring flanges I5 for use in mounting the apparatus on a wall or other suitable support. As an important feature of the invention, the adjacent edges of the side walls I3 and end walls I4 arespaced or unjoinedgwhereby to permit flexing of the end-walls it for an important purpose hereinafter noted. The end walls I4 are formed with inwardly opening sockets I6 for receivin the ends of the units I and 2. The ends of the units I and 2 are electrically insulated from the socketed end walls I4 by interposition of suitable sheet insulating material H. The normal space between the end walls I4 is somewhat less than the over-all lengths of the thermostat units I and 2 inclusive of the insulating material I1, and, therefore, in the assembly the end walls I4 are flexed apart to permit entry of the insulationequipped units I and 2 into opposed end wall sockets it, which end walls thereafter maintain the units I and 2 under yielding compression therebetween.

Because the device illustrated is a thermostat of the said rate of change type, the posts 4 and spring contact'strips of each of the units 1 and 2 are formed of the same thermally-responsive material, which may be assumed to be brass, for

example, so that under normal relatively slow rates of temperature change, regardless of how wide the range of change, the parts 4 and 5 will expand at substantially identical rates. However, the parts 4 and 5, although of the same material, involve vastly different volumes of such material, and, therefore, respond to rapid temperature changes at different rates. Hence, with the cooperating units l and 2 positioned as shown, an abnormally rapid rise in temperature will result in an increased outward bowing of the strip contacts 5, which will bring the same into circuit-making engagement at their longitudinal centers.

In Fig. 5, a cooperating pair of thermostat units i and 2 is shown as connected in what may be assumed to be a fire alarm circuit comprising a battery B having one side connected by a lead l8 to the terminal lug of the unit 2 and having its other side connected by a lead l9 to the terminal lug of the unit I through an interposed signal such as a bell 20.

Preferably, the adjacent edges of the side walls [3 and end walls [4 are quite widely spaced to provide for free air movement upwardly through the casing 3, and preferably, also, the front wall I2 is provided with ventilation apertures 2|.

What I claim is:

1. A thermostat comprising a pair of thermostat units, said thermostat units each comprising a rigid metallic post having laterally offset retaining flanges at opposite ends and a bowed flexible metallic strip confined between said opposite retaining flanges, and means mounting said units with their posts in laterally-spaced parallel relation and their bowed strips opposed for circuit-closing cooperation, each of said units being provided at one end portion with a terminal for a circuit lead, and said cooperating units being turned end-for-end one in respect to the other thereof, whereby to permit the use of identical units and to provide maximum spacing of the said terminals.

2. A thermostat comprising a pair of thermostat units, said thermostat units each comprising a rigid metallic post having laterally olfset retaining flanges at opposite ends and a bowed flexible metallic strip confined between said opposite retaining flanges, and means mounting said units with their posts in laterally-spaced parallel relation and their bowed strips opposed for circuit-closing cooperation, said mounting means being in the nature of a sheet metal casing having a front wall formed with laterallyprojecting side walls and end Walls, the adjacent edges of the end walls and side walls being spaced to permit free flexing of the end walls, said side walls being provided with projecting anchoring flanges and said flexible end walls being formed with laterally-spaced inwardly-opening sockets, the said cooperating thermostatic units each having its opposite ends seated in corresponding sockets of opposite end walls.

3. A thermostat comprising a pair of thermostat units, said thermostat units each comprising a rigid metallic post having laterally offset retaining flanges at opposite ends and a bowed flexible metallic strip confined between said opposite retaining flanges, and means mounting said units with their posts in laterally-spaced parallel relation and their bowed strips opposed for circuit-closing cooperation, said mounting means being in the nature of a sheet metal casing having a front wall formed with laterallyprojecting side walls and end walls, the adjacent edges of the end walls and side walls being spaced to permit free flexing of the end walls, said side walls being provided with projecting anchoring flanges and said flexible end walls being formed with laterally-spaced inwardly-opening sockets, the said cooperating thermostatic units each having its opposite ends seated in corresponding sockets of opposite end walls, and electrical insulating material interposed between the ends of said units and the sockets of the end walls.

4. A thermostat comprising a pair of thermostat units, said thermostat units each comprising a rigid metallic post having laterally offset retaining flanges at opposite ends and a bowed flexible metallic strip confined between said opposite retaining flanges, and means mounting said units with their posts in laterally-spaced parallel relation and their bowed strips opposed for circuit-closing cooperation, said mounting means being in the nature of a sheet metal casing having a front wall formed with laterallyprojecting side walls and end walls, the adjacent edges of the end walls and side walls being spaced to permit free flexing of the end walls, said side walls being provided with projecting anchoring flanges and said flexible end walls being formed with laterally-spaced inwardly-opening sockets, the said cooperating thermostatic units each having its opposite ends seated in corresponding sockets of opposite end walls, and electrical insulating material interposed between the ends of said units and the sockets of the end walls, the said end walls maintaining the said thermostatic units under yielding compression therebetween.

EINAR G. LOFGREN.

REFERENCES CITED UNITED STATES PATENTS Name Date Obermeyer et al. Apr. 17, 1945 Number 

